It is commonly known the fluid flow through perforations into a formation during a fracturing operation is not uniform. It is also well known that the resulting production is likewise extremely non-uniform, with a small fraction of the perforations producing the bulk of the production from the well. Efforts are ongoing to use targeted fracturing techniques to improve this situation by limiting the entry of fracturing fluid to specific locations in the well. However, a large number of wells already exist with poor distribution, and it may not be economically feasible to “refracture” such wells in a uniform manner.
Existing methods to measure the non-uniformity of production, and determine the distribution or map of relative producibility, include downhole flow measurement devices that can be positioned and used at multiple locations in the well, and straddle packer systems to produce a map from a specific area. Flow metering systems can be used to quantify how the total production flow of a well collects as the flow passes various perforations. This system is limited by the time required to get good quality data, the effect of the conveyance means on the well, and the resolution of the number of positions where data is collected. Straddle packer systems can be used to isolate a specific area in the well and produce it across a range of flow rates, yielding detailed information on this area. However, this means that at least part of the well has to be taken off of production, and the packer system and its conveyance is relatively slow and expensive to use.
The analysis of reflected pressure or tube waves has been used to detect a fracture or bottom irregularity in a well. Several references describe ways to analyze tube wave reflections, such as US 2011/0267922, US 2012/0018150, U.S. 61/923,216, and U.S. Pat. No. 7,819,188.
Additionally, the current state of the art for tracking the end of coiled tubing is measuring the length of coiled tubing deployed and using a tubing end locator, i.e., a set of sensors and physical down hole objects, such as a casing collar for ACTIVE™ coil that interacts with the coil to obtain a good reference position. Also, physical completion objects placed in the well that the coil can pull or push on help indicate its current depth. These tubing end locators have complicated issues associated with them, however, and do not always lead to a realistic depth measurement.
In the usual conditions, such tubing end locators can provide a good position reference accurate to about 3 m (10 ft) when the coiled tubing is being deployed down hole; however, this reference can become inaccurate when the coiled tubing motion is reversed. The calculation of the end of coil in vertical wells is easier because the tension on the coil is known, but the temperature in the wellbore can cause the coil to lengthen and/or balloon and introduce some inaccuracy. In horizontal wells, the end of coiled tubing does not move immediately when pulled on since it must overcome any helical or sinusoidal buckling before the end starts to move.
The industry has ongoing requirements for the development or improvement of methods, systems, and tools to determine the location and/or status of tools, fracture zones before, during, and/or after fracturing or refracturing operations, and/or such methods, systems, and tools that can be used in wells with or expected to have multiple open fracture zones.